Aircraft having a reduced acoustic signature

ABSTRACT

An aircraft the propulsive units of which include engines, and which is distinguished by reduced noise emissions, includes a wing structure fixed to an upper region of the fuselage, and a vertical tail system having at least two vertical stabilizers which are generally vertically fixed to the fuselage aftwardly of the wing structure. The engines are disposed side by side in a propulsive package disposed above the fuselage, which propulsive package includes the following, air inlet openings for the propulsive package, which openings are disposed above the fuselage between a point at the leading edge and a point at the trailing edge of an aerodynamic root chord of the wing structure; and exhaust nozzle conduit outlets associated with exhaust nozzle conduits, which outlets are formed by the structure (cowling structure) of the propulsive package, and are disposed above the fuselage forwardly of an aft terminus of the fuselage and between the vertical stabilizers.

BACKGROUND

1. Field

The disclosed embodiments relate to the area of technology of aircraft, particularly aircraft intended to take off and land from/onto runways in urban environments.

2. Brief Description of Related Developments

In particular, the disclosed embodiments relate to aircraft in civil aviation, wherewith it is proposed that an aircraft having an appropriate configuration of fuselage, various aerodynamic surfaces, and propulsion units, can achieve particularly low noise levels, favoring its use where noise control rules militate against the use of aircraft of conventional architecture, e.g. use in (over) urban areas.

Environmental considerations, particularly the burden of noise pollution to persons in the vicinity of airports when aircraft take off and land, are critical for the very survival of some airports located in heavily urban areas, where the balance of convenience to the users of the airport is yielding to the objections of the persons subjected to the noise.

In aircraft design engineering, therefore, the search for solutions providing lower noise levels is a constant challenge.

The principal sources of aircraft noise affecting airport environments are generally:

-   -   aerodynamic noise in the approach phase, particularly         aerodynamic noise generated by lift enhancing devices and         landing gear; and     -   noise from propulsion units, particularly during takeoff phases,         and particularly in the case of high speed aircraft.

Numerous attempts have been made to devise means of reduction of aerodynamic noise, and to design engines and engine housings (nacelles and other cowling structures) which are intrinsically less noisy.

Attempts to reduce aerodynamic noise by simplifying lift enhancing systems and by modifying airfoil and nose configurations are limited by the need for high lift coefficients.

Modern aircraft have engines which are, inter alia, less noisy. These engines are of the “turbofan” type, and employ very high dilution, generally greater than 5, which reduces the mean jet velocity of the engine and thereby the noise generated.

Such engines also have low noise nacelles and exhaust nozzles. E.g. a forwardly elongated nacelle has the effect of “masking” the noise radiated and propagated from air intake, at least in the direction of the ground. Also (or alternatively), such engines tend to mix core flow and fan air flow (the primary and secondary flows in the engine), e.g. with the use of suitable nozzles, which achieves noise reduction in that the core flow is the chief generator of noise.

However, the reduction in noise level which is obtained is often at the cost of increased engine complexity, increased weight, and decreased propulsive efficiency of the propulsive package, which can limit the feasibility of some solutions; moreover, the known solutions are still insufficient to meet future low noise requirements.

Another solution for reducing the noise impact on the ground of aircraft in flight involves locating the engines in locations and configurations such that the noise radiated from the air intakes and exhaust nozzles are “masked” by certain surfaces defined by structures of the aircraft.

In this connection, it has been proposed to mount the engines on the upper surface of the wing structure, achieved with the use of conventional engine nacelles mounted with the aid of vertical struts which extend between the respective engines and the top surface of the wing structure.

With such an arrangement, the wing surfaces forwardly of and also laterally of the engine air intakes create a “mask” which limits propagation of noise toward the bottom (of the aircraft) and thus toward the ground, when the aircraft is in flight. However, such positioning of the engines where conventional engine nacelles are employed is not sufficient to significantly reduce emitted and propagated noise, particularly toward the rear.

Solutions of the type described above have only rarely been implemented in practice on aircraft.

SUMMARY

According to the invention, it is proposed to employ an aircraft architecture which is optimized to substantially reduce the noise emitted by the engines and to “mask” the noise so emitted so that it is minimally propagated to the ground.

The proposed low noise aircraft has the following features of conventional aircraft: a fuselage, a wing structure fixed to the fuselage, at least one horizontal stabilizer, a vertical tail system, and one or more propulsion engines.

To provide an optimum “mask” against radiation and propagation of acoustic waves toward the ground when the aircraft is in flight, without the addition of specific devices, the configuration and arrangement of the wing structure, the vertical tail system, and the one or more reactors, with respect to the fuselage, are such that:

-   -   The wing structure is fixed to the fuselage in an upper portion         of said fuselage;     -   The vertical tail system is comprised of at least two vertical         stabilizers which are generally vertically mounted on the         fuselage aft of the wing structure;     -   One or more propulsion engines are provided, which (if more than         one) are disposed side by side in a propulsive package disposed         above the fuselage, which propulsive package is comprised of the         following:         -   air intake openings for said engine(s), which openings are             formed by a structure (cowling structure) of said propulsive             package, which openings are disposed above the fuselage and             extend along a longitudinal axis of the fuselage between a             point at the leading edge [sic] and a point at the trailing             edge [sic] of an aerodynamic root chord of the wing             structure), with respect to the fuselage [sic]; and         -   exhaust nozzle conduit outlets, which exhaust conduit             outlets are formed by the structure (cowling structure) of             the said propulsive package, and are disposed above the             fuselage forwardly of an aft terminus of said fuselage and             between the vertical stabilizers.

In order to facilitate integration of the propulsive package with the fuselage, the width of the fuselage in the aftmost portion is equal to or greater than the width of the propulsive package, and the vertical stabilizers are generally in aerodynamic continuity with the lateral external walls of the structure (cowling structure) which structure accommodates the propulsive package.

In order to obtain effective “masking” of noise radiated by the

-   -   engine air intakes, the air intake openings of the propulsive         package are disposed above the fuselage, along the longitudinal         axis of said fuselage, preferably near a point with respect to         the root chord (of the wing structure), such that the area of         the acoustic “mask” created by the wing structure is maximized         in light of the noise radiation and propagation diagrams for         noise from the air intakes and from the leading edge sweep of         the wing.

To improve the aerodynamic integration of the propulsive package, and to enhance “masking” against radiation and propagation of noise from the engine air intakes, the engines are installed in a sunken position, such that at least 10%, advantageously c. 30%, of the diameter of each engine is disposed below the upper delimiting surface of the fuselage.

To improve the noise reduction at the front and rear of the engines, at a least a portion of the interior surfaces of the structure (cowling structure) of the propulsive package, which interior surfaces generally extend from air intakes and exhaust nozzles of the propulsive package, have means of/for absorption of acoustic waves.

To provide an effective “mask” against noise emitted by the exhaust nozzles, the exhaust nozzle conduits (conduit outlets) which are formed by the structure (cowling structure) of the propulsive package, are disposed (reckoned in the direction of the longitudinal axis of the fuselage) aft of the leading edges of the vertical stabilizers and forwardly of the trailing edges of said vertical stabilizers.

Advantageously, the relatively large length of the propulsive package allows the engines to be disposed in a more or less aftward location, without degrading the performance of the proposed configuration, wherewith in particular the engines are disposed at a locus with respect to the longitudinal axis of the fuselage, such that zones of ejection of debris from the engines will not affect zones of the wing structure or of the stabilizers where organs which are important for the safety of the aircraft are disposed.

As a result of the width of the fuselage in the zone of the propulsive package, the engines are suspended (mounted) under a part of the structure (cowling structure) which is fixed with respect to the fuselage, and are disposed above maintenance shafts which traverse an aft portion of the fuselage, which shafts generally extend vertically with respect to said engines. These maintenance shafts facilitate raising and lowering of the engines at times when the engines are being mounted and demounted.

Advantageously, the fixed structure (cowling structure) of the propulsive package comprises one or more separation walls between the engines, which walls extend aftwardly from a zone of the air intake to a zone of the exhaust nozzle, so as to provide appropriate shielding (armoring or the like) suitable for protecting an engine from debris which might be ejected from a neighboring engine. Said separation walls support swingably mounted covers which are adapted to engine maintenance needs.

There follows a detailed description of some exemplary embodiments of the invention, with reference to the drawings, which are schematic illustrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inventive aircraft with its landing gear extended;

FIG. 2 is a plan view of the aircraft of FIG. 1;

FIG. 3 is a lateral profile view of the aircraft of FIG. 1;

FIG. 4 a is a frontal view of the aircraft of FIG. 1;

FIG. 4 b is a rear view of the aircraft of FIG. 1;

FIGS. 5 a and 5 b are a frontal perspective view and a rear perspective view, respectively, of details of the configuration of the aft portion of the fuselage of the inventive aircraft;

FIG. 6 is a plan view of the aft portion of the aircraft of FIG. 1, illustrating zones of potential ejection of debris from the engines [sic]; and

FIGS. 7 a and 7 b are a perspective view and a lateral profile view, respectively, of an aft portion of the aircraft of FIG. 1, illustrating the jet engines in different positions during maintenance operations on said engines.

The present description of a preferred embodiment of the invention is offered merely by way of example, and does not limit the scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

As illustrated in FIG. 1 an inventive aircraft 1 is comprised of a fuselage 10, a wing structure 20, a horizontal stabilizer 30, a vertical tail system 40, and a propulsive package 50 comprising jet engines, which package 50 is mounted over the aft portion of the fuselage 10.

For the purposes of description, the following conventional coordinate system will be used:

-   -   The X axis is an axis parallel to the longitudinal axis of the         fuselage, and directed toward the front of the aircraft [i.e.         the positive ray of the X axis is in the forward direction];     -   The Z axis is perpendicular to the X axis and parallel to a         vertical plane of symmetry of the aircraft, and is directed         downward;     -   The Y axis is perpendicular to the plane defined by the X and Z         axe, and is directed toward the starboard side of the aircraft.

The lateral extent of the wing structure is thus essentially in the Y direction, the longitudinal extent of the fuselage is essentially in the X direction, and the lateral extent of the fuselage is essentially in the Y direction.

The aircraft 1 illustrated in FIGS. 1-4 has certain characteristics which together promote quietness of operation of the aircraft.

A first characteristic relates to the wing structure 20. The wing structure on the aircraft 1 is fixed at an elevated position on the fuselage.

A second characteristic relates to the vertical tail system 40.

In conventional fashion, said vertical tail system is disposed in (on) the aft portion of the fuselage.

This particular vertical tail system is comprised of a pair of vertical stabilizers (41 a, 41 b) which comprise generally vertical aerodynamic surfaces which are fixed in a generally symmetrical manner with respect to a vertical plane of symmetry XZ of the fuselage and are mutually separated by a distance Yv in the Y direction.

A third characteristic relates to the horizontal stabilizer 30.

This horizontal stabilizer is an aft structure, i.e. is disposed aft of the wing structure 20 with regard to the direction of flight of the aircraft, and is essentially comprised of a generally horizontal aerodynamic surface which is fixed at an elevated region of the vertical stabilizers (41 a, 41 b).

In known fashion, the vertical stabilizers (41 a, 41 b) and the horizontal stabilizer 30 are provided with, respectively, deflectable rudders for rudder control (yaw control) in relation to the vertical tail, and deflectable elevator flaps for pitch control in relation to the horizontal stabilizer; these control surfaces are preferably disposed at the trailing edges of their respective stabilizer surfaces, and they serve to control the aircraft, particularly in flight.

A fourth characteristic relates to the propulsive package 50.

The propulsive package 50 comprises the complement of propulsion units (engines) used to propel the aircraft. In the example illustrated in the drawings, two engines (51 a, 51 b) are arranged in the propulsive package 50; in variant embodiments a larger number of engines is possible, e.g. three or more, provided that (as will be discussed infra) a constraint is imposed on:

-   -   the width of the fuselage in the zone of the propulsive package;         and     -   the [separation] distance Yv.

A propulsive package comprised of a single engine is possible, but is impracticable because of safety considerations.

The propulsive package is disposed above the fuselage 10 between the wing structure 20 and the vertical tail system 40.

The propulsive package comprises the engines, which are advantageously disposed side by side with their axes parallel, and further comprises a cowling structure 52 which generally surrounds the engines.

This cowling 52 is equivalent to a nacelle (engine pod), with a generally barrel-like shape, mounted around the engines; this is analogous to the means of mounting of engines on a conventional aircraft [sic], wherein a given engine is mounted on a lift strut which attaches it to an airfoil or to the fuselage.

A forward part of the cowling structure has (comprises) air intakes (air intake conduits) 53 for the engines (51 a, 51 b); and an aft part of the cowling structure has exhaust nozzle conduits 54 for said engines.

Between the forward border of the air intakes 53 and the aft border of the exhaust nozzle conduits 54, the cowling structure 52 defines surfaces which provide aerodynamic continuity of the shape of the propulsive package 50:

-   -   at the exterior of the propulsive package, to minimize external         aerodynamic drag; and     -   interiorly of the propulsive package, to provide aerodynamically         favorable flow patterns from points appreciably ahead of and         behind the engines, in order to ensure good operation of the         engines and good propulsive efficiency and output. The internal         configurations of the cowling structure 52 should conform to         known principles for engine air intakes and engine exhaust         nozzles, wherewith in particular the surfaces should be of good         “surface quality”, and at all points the cross sections of the         conduits for said air intakes and exhaust nozzles should be well         adapted to the engines employed.

Advantageously, the external shape of the cowling structure 52 should be optimized for minimum fuselage drag.

The said external shape evolves progressively from the forward border of the air intakes 53 (concerning which the aerodynamic constraints of good functioning of the engine air intake system are a factor) to the shapes of the connections of and to the vertical stabilizers (41 a, 41 b), with lateral walls being generally vertical and advantageously having upper wall shapes which are relatively flattened, defining, e.g., an aerodynamic channel of generally constant cross section or of a cross section which varies in a controlled manner, bounded vertically by said upper wall of the cowling and the horizontal stabilizer 30, and bounded horizontally by the two vertical stabilizers.

Compared to a conventional reactor nacelle, the cowling structure 52 is proportionally longer in relation to the length of the engines (51 a, 51 b). This increased length does not come at the cost of any appreciable increased weight, because the mounting of the cowling structure above the fuselage 10 means that said cowling structure is supported over its entire length, without a cantilever structure, and without the need for reinforcement, because substantial strength and stability is contributed by the fuselage, which fuselage is already dimensioned to withstand appreciable loads.

According to a particularly advantageous embodiment, the engines (51 a, 51 b) are disposed at a lower altitude on the coordinate axis Z, i.e. are shifted downward (in the positive Z direction) (sunken to some extent) toward the bottom of the aircraft, such that a portion of the reactors is disposed below the line delimiting the upper surface of the fuselage 10 proper (FIG. 4 a).

By mounting the engines at a lower altitude on the aircraft, wherewith e.g. 30% of the diameter of a given engine is below the upper delimiting surface of the fuselage 10 (in any event at least 10% of said diameter), the maximum cross section of the fuselage in the zone of the engines is generally reduced, thereby reducing the overall aerodynamic drag contribution of the propulsive package.

In order to compensate for the described mounting of the engines at a lower altitude on the aircraft, the cowling structure 52 is shaped such that the air intake configuration (air intake conduit) for the engines redirects and delivers air in the Z direction from a zone above the fuselage to the air intakes proper of the engines, wherewith necessarily the air intake conduit has a generally “S” shape.

This particular configuration of the air intake conduit, and the shifted (sunken) position of the engines, also favors radiation and propagation of the noise of the air intake in a direction opposite to the ground, and thereby contributes to reduction of the noise at ground level.

The extent of the cowling structure 52 in the forward direction (positive X direction) is delimited by the air intake openings 53 which, as seen, are disposed above the fuselage 10 but are in a zone of the fuselage which corresponds to [sic] the zone of the fuselage in which the wing 20 is attached to the fuselage.

More particularly, if one considers a wing chord 21 corresponding to [sic] a chord located close to the fuselage, known as the “root chord”, the air intake openings 53 preferably are disposed (with regard to the X axis) between a point at the forward of said chord and a point at the aft end of said chord (the front being directed toward the direction of forward travel of the aircraft).

With these relative positions of the wing structure, the fuselage, and the air intake openings, it is seen that the combined surface above the fuselage 10 and the wing structure 20 forms a “mask” [sic], represented by the shaded zone in FIG. 2, which mask tends to resist propagation of noise radiated by the air intakes toward the bottom of the aircraft, thus toward the ground when the aircraft is aloft.

A preferred disposition of the air intake openings of the propulsive package 50 along the longitudinal axis, with respect to the root chord 21, which intake openings are located above the fuselage, is obtained if the acoustic “mask” 22 (represented by the shaded zone in FIG. 2) created by the wing structure 20 is optimized (“maximized”) in light of the noise radiation and propagation diagrams for noise from the air intakes and from the leading edge sweep of the wing 20.

Advantageously, the efficiency and efficacy of the reduction in noise emitted toward the front of the engines is also improved if the following features are present:

-   -   the air intake conduits, defined by an interior surface of the         cowling structure 52 disposed between the front end of said         structure and an intake plane of the engines (51 a, 51 b), are         relatively long with respect to the diameter of the engine air         intakes [sic];     -   the air intake conduits have acoustic absorption means (“an         acoustic absorption treatment”) similar to known absorption         means used for engine air intakes, but in this case applied to a         greater surface, in view of the length of these conduits;     -   the air intake openings themselves are inclined rearward, i.e.         the upper lip of the air intake openings is disposed rearward         from the lower lip, having the effect of blocking downward         propagation of noise toward the bottom of the aircraft, and thus         toward the ground, when the aircraft is aloft.

The extent of the cowling structure 52 in the aftward direction (negative X direction) is delimited by the exhaust nozzle conduit outlets 60 (FIG. 5 b), which the upper portion of the cowling structure terminates.

With this relationship between the cowling structure 52 and the exhaust nozzle conduit outlets 60, the cowling structure 52 has the following configurational features:

-   -   the exhaust nozzle conduit outlets 60 are disposed above the         fuselage 10, forwardly of the aft terminus of the fuselage;     -   said exhaust nozzle conduit outlets 60 are disposed between the         vertical stabilizers (41 a, 41 b), namely aft of the leading         edges which are at the front of said vertical stabilizers and         forwardly of the trailing edges which are at the aft end of said         vertical stabilizers. Preferably the exhaust nozzle conduit         outlets are disposed close to but nonetheless aft of said         leading edges of the vertical stabilizers;     -   the lateral parts of the cowling structure which parts for         exhaust conduits 54 define surfaces which are in continuity with         the lateral surfaces of the vertical stabilizers (41 a, 41 b).

In such an arrangement, the exhaust conduits between [sic] the rear exhaust loci of the engines (51 a, 51 b) and the exhaust conduit outlets are longer than in a conventional engine nacelle; this enables better mixing of the primary and secondary streams of the engines, and enables improved treatment at the internal walls of the cowling structure 52.

For the purposes of such a configuration of the propulsive package 50 and the vertical stabilizers (41 a, 41 b), it is provided that an aft portion 12 of the fuselage 10, extending generally from the location of the air intake opening 53 to the aft terminus 11, which portion at least partly comprises a zone of changing shape and cross section in which, with progression in the aft direction, the fuselage cross section changes from a cross section corresponding to a substantially cylindrical fuselage zone 13, to a relatively thin aft terminus (11), with the aim of limiting the aerodynamic drag effects which would occur if the fuselage had a blunter aft portion, and at the same time the fuselage must be large (wide etc.) enough to permit installation of the propulsive package with the characteristics which will be described infra.

Thus, the width of the fuselage in the aftmost portion 12 is at least equal to the width of the propulsive package 50, and in the zone where the vertical stabilizers (41 a, 41 b) are mounted said width must be at least equal to Yv, and sufficient to accommodate maximum widths of the engines (51 a, 51 b), and in addition sufficient to satisfy the structural requirements for installation of the vertical stabilizers (41 a, 41 b); these dimensioning considerations will depend on the technological means of assembly and on the materials utilized.

Advantageously, the width of the fuselage in the cylindrical region 13 is chosen in relation to the diameter of the engines and thus in relation to the width of the propulsive package 50; in connection with this, the fuselage 10 will have a somewhat uniform width right to its aft terminus 11, in particular a width generally equal to that of the cylindrical fuselage region 13.

According to the proposed configuration, an “extension” 110 of the fuselage and the vertical stabilizers in the X direction aftward of the exhaust nozzle 60 may be provided, which creates an acoustic “mask” against noise radiated and propagated from said exhaust nozzle.

Advantageously, the longitudinal position (in the X direction) of the engines (51 a, 51 b) is chosen such that any ejection of debris from an engine in the event of breaking up of parts or assemblies in the engine will not risk damage to essential organs of the aircraft.

In FIG. 6, the arrangement has been chosen such that the ejection cones (71, 72) of engine debris do not involve (intersect) elements such as airfoil surfaces, roll control surfaces, yaw control surfaces [(rudder)], or pitch control surfaces, or internal organs which if damaged might comprise flight safety.

As illustrated in FIGS. 7 a and 7 b, to facilitate maintenance of the engines (51 a, 51 b), the cowling structure 52 has movable housing elements 522, e.g. swingable hatch elements (housing flap elements), which when opened enable access to the engines from above the fuselage 10, for inspection or routine maintenance.

Preferably, said movable housing elements 522 are swingably mounted on one or more structural separation walls between the engines (51 a, 51 b) which walls are fixedly mounted on the fuselage and which extend longitudinally from a zone of the air intake to a zone of the exhaust nozzle. Advantageously, in the zones of the engines where a risk is present that debris will be ejected from an engine in the event of breaking up of parts or assemblies in the engine, said separation walls have protective means (armoring or the like) suitable for protecting an engine from debris which might be ejected from a neighboring engine.

Advantageously, the engines are suspended (mounted) under a fixed part 521 of the cowling structure 52, which part 521 preferably is solidly attached to the structural separation walls between the engines, said mounting being via engine struts (not shown); and vertical maintenance shafts 121 are provided in the fuselage generally below the engines, to facilitate installation and de-installation of the engines with the aid of conventional hoist means which are fixed to the engine struts during the maintenance operations.

When maintenance is not being performed, the maintenance shafts 121 are covered by upper and lower hatches (e.g. 122) which preserve the aerodynamic continuity of the fuselage.

Thus, by judicious choice of the arrangement and configuration of various essential organs of the aircraft, in particular involving the fuselage, the wing structure, the vertical tail system, the horizontal stabilizer, and the propulsive package, one achieves an aircraft which when in flight transmits substantially less noise to the ground than does a conventional aircraft. 

1. An aircraft, comprising a fuselage, a wing structure fixed to the fuselage, at least one horizontal stabilizer, a vertical tail system comprised of at least two vertical stabilizers which are generally vertically mounted on the fuselage aft of the wing structure, and one or more propulsion engines which (if more than one) are disposed side by side in a propulsive package disposed above the fuselage, which propulsive package is comprised of the following: air intake openings for said engine(s), which openings are formed by a cowling structure of said propulsive package, which openings are disposed above the fuselage and extend along a longitudinal axis of the fuselage between a point at the leading edge sand a point at the trailing edge of an aerodynamic root chord of the wing structure, with respect to the fuselage; and exhaust nozzle conduit outlets associated with exhaust nozzle conduits, which outlets are formed by the cowling structure of the said propulsive package, and are disposed above the fuselage forwardly of an aft terminus of said fuselage and between the vertical stabilizers; wherein the vertical stabilizers are generally in aerodynamic continuity with the lateral external walls of the cowling structure which structure accommodates the propulsive package.
 2. An aircraft according to claim 1, wherein the width of the fuselage at an aft terminus is equal to or greater than a width of the propulsive package.
 3. An aircraft according to claim 2, wherein the exhaust nozzle conduit outlets associated with exhaust nozzle conduits, which outlets are formed by the cowling structure of the propulsive package, are disposed of the leading edges of the vertical stabilizers and forwardly of the trailing edges of said vertical stabilizers.
 4. An aircraft according to claim 1, wherein each of the air intake opening(s) is inclined rearward, wherewith an upper lip of said opening is disposed aftwardly of a lip in the base portion of said opening.
 5. An aircraft according to claim 1, wherein the engines are installed in a sunken position, such that at least 10% of the diameter of each engine is disposed below the upper delimiting surface of the fuselage.
 6. An aircraft according to claim 1, wherein interior surfaces of the cowling structure of the propulsive package, which interior surfaces generally extend from air intakes and exhaust nozzles of said propulsive package, have means of/for absorption of acoustic waves.
 7. An aircraft according to claim 1, wherein the horizontal stabilizer has a generally horizontal aerodynamic surface which is fixed to an upper portion of the two vertical stabilizers.
 8. An aircraft according to claim 1, wherein the engines are disposed at a locus with respect to the longitudinal axis of the fuselage, such that zones of ejection, of debris from the engines will not affect zones of the wing structure or of the stabilizers where organs which are important for the safety of the aircraft are disposed.
 9. An aircraft according to claim 1, wherein the engines are suspended under a fixed part of the cowling structure, above maintenance shafts which traverse an aft portion of the fuselage, which shafts generally extend vertically with respect to said engines.
 10. The aircraft according to claim 3 wherein the exhaust nozzle conduit outlets are reckoned in a direction of the longitudinal axis of the fuselage.
 11. The aircraft according to claim 6 wherein the interior surfaces are disposed at and near the air intakes and exhaust nozzle. 